DE1517226C - Process for the production of high purity Zeil material - Google Patents

Description

A high degree of purity is required of a pulp used for chemical purposes, d. H. low pentosan content and low alkali solubility. Pulps of this type are made from Wood produced by sulphite boiling or by means of pre-hydrolysis and sulphate boiling (US Pat. No. 1 880043). In the latter case, the wood is heated under pressure with water or dilute mineral acids. During this process, part of the hemicellulose in the wood is dissolved. To the pre-hydrolysis Ordinary sulphate boiling joins in to dissolve lignin and a substantial part of the hemicellulose on. When cooking sulfite, both lignin and hemicellulose are dissolved. By heating with alkaline Solutions, usually dilute sodium hydroxide, but also sodium carbonate, can be used Pulp can also be cleaned. Sulphite cooking was also combined with alkaline cooking Cleaning stage in such a way that the sulphite boiling is interrupted as soon as the lignin in the wood is sulfonated enough to be dissolved by alkali, and then, with or without Removal of the sulphite cooking acid used, alkali introduced into the cooker. Characteristic for this on The usual sulphite-based pulp production process is that one does the cooking with initiates an acidic stage using those required to sulfonate and dissolve the lignin Amount of sulphite cooking acid, which contains sulfur dioxide and metal sulphite.

From the Austrian patent specification 194238 is a process known in which the prehydrolysis is carried out with the aid of sulfur dioxide and this is followed by an alkaline boiling in which no sulfite is present.

The products obtained by the known processes are satisfactory in terms of their chemical properties Purity not yet complete. The aim of the invention is therefore to create a method which to a derivative-type pulp with high chemical purity.

The inventive method for the production of high purity pulp, in which wood in a first stage subjected to a non-delignifying pre-hydrolysis and in a subsequent stage with an alkaline cooking liquid is digested, is characterized in that the effective chemicals the alkaline cooking liquid is at least 50% soluble sulfite and also as usual a sulfide and / or a hydroxide and / or a carbonate contain.

There is also a process known in which after the prehydrolysis of the wood chips in a In the second process step, the chips with sulphite-rich solutions at a pH value between 3 and 9 treated, after which the boiling is carried out in an acidic medium. Here will be Pulps received that contain a multiple of impurities, especially pentosan, compared to Invention included.

The manufacture of paper stock by cooking in a weak alkaline medium containing sodium sulfite and sodium sulfide is known, inter alia from an article by Peckham and van Drunen published in TAPPI, Vol. 44, No. 5, pp. 374 to 384 (1961). According to this previously known method, a typical composition of the cooking liquid consists of sodium sulfite corresponding to 6% sulfur dioxide, 1% sodium carbonate and 1% sodium sulfide. This cooking process results in a paper stock that exceeds that of paper stocks cooked by other cooking processes in terms of burst strength, tear strength and tear length. According to the article mentioned, the chemical analysis of such a paper stock showed a pentosan content of about 9% and an alpha cellulose content of about 84% Pentosan contents that are 1 to 2% below those obtained by pre-hydrolysis with subsequent sulphate boiling. In addition, the new cooking process resulted in a higher viscosity pulp. Thanks to the invention, pentosan contents below 0.9% can be achieved, which according to the process consisting of prehydrolysis and sulphate boiling is only possible with the inclusion of alkaline refinement.

Water can advantageously be used for the prehydrolysis, but are also suitable weak organic acids such as acetic acid, or mineral acids such as sulfuric acid, or sulphurous Acid in a small amount. The aqueous solutions of the acids should expediently have an acid content have a maximum of 2%.

The waste liquor from the alkaline cooking can be useful for the preparation of new cooking liquid serve, or sodium and sulfur can be recovered for the preparation of new cooking liquid will.

In the pulp produced by the process of the present invention, the alkali solubility and in particular the pentosan content is lower than in the known combination of prehydrolysis and sulphate boiling. In addition, the viscosity of the pulp can be significantly higher. This result is surprising and could not be foreseen. The invention is described in more detail in the following examples, with example 1 relating to the known combination of prehydrolysis and sulphate boiling. In the examples, the lignin content is determined as the kappa value according to SCAN-Cl: 59, the viscosity was determined according to TAPPI 206, calculated from CCA 28: 57, pentosan according to CCA 24: 57 and the alkali solubility was determined in 10 and 18 _% igem NaOH, RIO or R18 determined according to SCAN-C 2:61. The temperatures in the examples are given in degrees Celsius.

Pre-hydrolysis

Pine chips were mixed with water in a ΙΌ-1 autoclave with a wood-to-liquid ratio heated from 1: 4 under different conditions. This resulted in three different types of pre-hydrolyzed Shavings. After the cooking liquid had been drained off, the chips were used for cooking attempts without being washed used.

Time to increase the temperature in minutes from 20 °
_6j maximum temperature ^

Rest time at maximum temperature
in minutes

designation

Maximum temperature, ⁰ C 150 170

102

13th
A.

126

126

Alkaline cooking

Chemical loading, cooking temperature and time have been changed. All chemical loading is on calculated per 1 kg of dust-dry original wood.

Example 1

The three types of pre-hydrolyzed wood were cooked using the well-known sulphate method. Wood-liquid ratio 1: 4. The cooking temperature was raised to 215 minutes from 80 to 170 ⁰ C and held for 100 minutes at this value. The unbleached pulp was analyzed

Applied

pre-hydrolyzed chips. .

NaOH, g / kg

Na ₂ S, g / kg

Na ₂ CO ₃ , g / kg

Kappa value

Viscosity. cP

Pentosan, ^{0 /}

R 10

R18 ....

/ ο

attempt

la

A 128

82

47

28

102

5.0 91.3 93.2

Ib Ic B. C. 25th 128 80 82 46 47 15th 11th 69 28 2.9 1.8 93.S. 95.3 95.4 97.2

B e i s ρ i e 1 2

The three different pre-hydrolyzed wood samples were used as starting material were cooked according to the invention. After heating to 130 ° and resting at this temperature of 60 minutes the temperature was increased to 180 ° over 156 minutes and for the following specified time held at this value. Wood to liquid ratio 1: 5.

Applied

pre-hydrolyzed

Shavings

Na ₂ SO ₃ , g / kg

Na ₂ CO ₃ , g / kg

Na ₂ S, g / kg

Rest time at 180 °

Minutes

pH before cooking
pH after

Cook

Kappa value

Viscosity, cP

Pentosan,%

RIO

R18

attempt

2a

610
50
50

140
12.6

9.2
23
76

3.2
94.0
95.2

2 B 2c B. C. 610 610 50 50 50 50 160 190 12.6 12.6 9.3 9.4 20th 30th 49 28 1.7 0.9 95.5 97.0 96.7 98.3

610

50

190

12.5

9.3 24 20

1.0 96.4 98.0

Example 3

Prehydrolyzed wood according to B above was made according to the invention with various loads cooked. After heating to 130 ° and resting for 60 minutes at this temperature, the Temperature increased over 130 minutes to 170 ° and for the time indicated below on this Value held.

Na ₂ SO ₃ , g / kg

Na ₂ CO ₃ , g / kg

Na ₂ S, g / kg

Rest time at 170 °, minutes

pH before cooking

pH after boiling

Kappa value

■ Viscosity, cP

Pentosan,%

RIO

R 18

attempt

3a

485

39

80
420

12.8
9.6

26th
105
1.5

96.4

97.1

3b 3c 610 975 50 80 50 80 420 280 12.6 - 9.4 10.0 20th 22nd 62 97 1.7 1.5 95.8 96.4 96.3 97.3

Example 4

The starting material used was pre-hydrolysed wood according to C, which varied the sulphide charge considerably was cooked. Wood to liquid ratio 1: 5. After resting for 60 minutes at 130 °, the temperature increased for 145 minutes increased to 175 ° and held at this value for 290 minutes in experiment 4a. In experiments 4b and 4c after the resting time, the temperature was increased to 170 ° for 110 minutes and for 390 minutes held at this value.

Na ₂ SO ₃ , g / kg

Na ₂ CO ₃ , g / kg

Na ₂ S, g / kg

Sieve residue,%

pH before cooking.
pH after boiling

Kappa value

Viscosity, cP

Pentosan,%

R 10

R 18

attempt 4a 4b 610 610 0 82 100 25th 1.7 7.3 - . 12.7 9.5 9.3 40 47 36 36 0.9 0.9 97.2 97.3 98.3 98.0

610

165

9.7 11.5 9.1
62

1.0 96.9

97.7

Example 5

Pine chips were prehydrolyzed with water in a 10 liter autoclave. The time for the temperature to rise to 170 ° was 120 minutes and the holding time at this temperature was 23 minutes. After removing excess cooking liquid, the following were used per kilogram of original wood: 640 g Na ₂ SO ₃ , 25 g Na ₂ CO ₃ and 80 g Na ₂ S. After the resting time at 120 °, the autoclave was heated to 175 ° for 65 minutes and then for Maintained at this temperature for 410 minutes. After boiling, the pH was 10.5. A residue of 1.6% remained on sieving. The pulp had the following analysis: Kappa value 9, viscosity 36 cP, pentosan 1.1, RIO 97.2 and R 18 98.0.

Bleaching

The bleaching of the pulps obtained according to the invention does not cause any difficulties. The bleaching can be used in several stages with chlorine dioxide without any appreciable loss of viscosity or as required final viscosity can be done using bleaching sequences which are a viscosity regulating hypochlorite stage lock in. The following may be given as an example of bleaching:

cellulose example according to 5 4a 18th Chlorination, 20 °, 1 hour, g / kg 80 Alkaline wash, 1 hour, 45 Temperature ° C 70 13th Feeding NaOH, g / ka 25th Sodium hypochlorite, 35 °, pH 10.5 2.5 1 hour, active chlorine, g / kg 10 4.5 Chlorine dioxide, 65 °, 3 hours, pH 3.6 4th Active chlorine, g / kg 10 Alkaline washing, 80 °, 40 minutes 5 Feed NaOH. g'kg .... - 4.2 Chlorine dioxide, 65 °, 2.5 hours, pH - 5 Active chlorine, g / ks - Sodium hypochlorite, 35 ', 2 hours of active chlorine, g / kg 4th g / kg 5 Sulfur dioxide treatment. 20 ", 10 σ / kg 10

Viscosity, cP

Pentosan,%

RIO

R 18 ....

Brightness, SCAN CIl: 62

cellulose
according to the example

4a

20th
0.9
96.9
98.1

25th

1.1
97.1
98.0
89.3

IO

35

The load refers to pulp in a dust-dry state. Between each bleach stage a water wash was put in place. The pulp concentration in the chlorine level was 3% and in the remaining levels 5%

Pulp analysis

45

As can be seen from the above examples, the cooking temperature, cooking time and chemical loading can be varied. It is thus preferable to use 485 to 975 g / kg Na ₂ SO ₃ , although the amount charged can be reduced to 300 g / kg, provided that a sufficient amount of sulfide is present. The upper limit for Na ₂ SO ₃ corresponds essentially to economic considerations. It can be seen from Examples 1 and 2 that a change in the prehydrolysis results in pulps with a significantly lower pentosan content than is achieved with sulphate cooking. Example 3 makes it clear that the sulfite charge can be varied within wide limits and that high viscosities can be obtained with low pentosan contents. It can be seen from Examples 2d and 4a that sodium carbonate can be omitted. In alkalis used in practical use, however, the sodium carbonate can hardly be avoided, and even a high content of it does no harm. Example 4 shows the importance of sodium sulfide. The amount of Na ₂ S is expediently 25 to 200 g / kg, preferably 50 to 100 g / kg. 100 g / kg of dry wood are advantageous (cf. 4 a with 2 c and 2d). A decrease to 25 g / kg (4 b) or a complete omission (4 c) results in a pulp with a high kappa value, which is difficult to defibrate and which results in a high sieve residue. In all the other cases mentioned here, the sieve residue was below 2%. Experiments have also been carried out with the addition of sodium hydroxide. Under the same conditions as in Example 4, Experiment 4b, in addition to the chemicals indicated, free sodium hydroxide was added in an amount equal to 25, 50 and 100 g per kilogram of dry wood. The cooking time could be shortened considerably and a high degree of purity of the pulp could still be obtained. The pentosan content was at most 1.1% ^and the RIO and R 18 exceeded 97.0 and 98.0%, respectively, which are significantly better results than those with the corresponding sulphate boiling described in experiment 1c.

The examples make it clear that cooking prehydrolyzed wood with alkaline sodium sulfite and changing conditions in all cases examined pulp with a pentosan content which is significantly lower than that obtained when cooking the same pre-hydrolyzed chips obtained by the sulfate method. The invention is not restricted to those given in the examples Cooking conditions. The prehydrolysis can of course at other temperatures and on Carry out spot of water with dilute acids or steam. For those specified in the Examples of feeds used, the sodium sulfide was largely consumed, while the sodium sulfite remains partially unchanged. A large part of the waste liquor can therefore can be used to advantage for the preparation of the cooking liquid, reducing the consumption of chemicals is lowered. For the effect obtained it is essential that the cooking liquid is the main component Contains sodium sulfite and that the addition of sodium sulfide lowers the kappa value and one easy to defibrate pulp, which makes it easier to achieve high viscosity. for For the practice of the invention it is important that the cooking process involve chemical recovery a known type is combined, which is the recovery of sodium and sulfur in the form of sodium sulfite and sodium sulfide allowed.

Claims (1)

Claim: Process for the production of high-purity pulp, in which the wood is in a first stage a not subjected to delignifying pre-hydrolysis and in a subsequent stage with an alkaline Cooking liquid is digested, thereby characterized in that the effective chemicals of the alkaline cooking liquid at least 50% a soluble sulfite and also, as usual, a sulfide and / or a hydroxide and / or contain a carbonate.